Cobalt base alloys containing molybdenum



March 29,

Filed sept.

YIELD STRENGTH KS I I I (/o RA) DUCTILITY 1966 J. J. RAUSCH ETAL3,243,289

COBALT BASE ALLOYS CONTAINING MQLYBDENUM 24, 1963 2 Sheets-Sheet 1 ROOMTEMPERATURE o l l I l I ROOM TEMPERATURE O l l l l l l l 5 IO 15 2O 253O SOLUTE ADDITION (WEIGHT PERCENT) TE NSILE PROPERTIES OF COBALTALLOYED WITH MOLYBDENUM FIG.

INVENTORS JOHN J. RAUSGH JOSEPH a. McANDREW BY ATTORNEY WIQ March 29,1966 J, uscH ETAL 3,243,289

COBALT BASE ALLOYS CONTAINING MOLYBDENUM Filed Sept. 24, 1963 2Sheets-Sheet 2 YIELD STRENGTH, PSI

REDUCTION IN AREA ALLOY ADDITION (WEIGHT PERCENT) THE EFFECT OF TERNARYADDITION ELEMENTS ON THE I700F TENSILE PROPERTIES OF THE BASE GOM-POSITION= Go-l5Mo.

United States Patent 3,243,289 COBALT BASE ALLOYS CONTAINING MOLYBDENUMJohn J. Rausch, Evanston, IlL, and Joseph B. McAndrew,

Pittsburgh, Pa., assignors, by mesne assignments, to

the United States of America as represented by the Secretary of the NavyFiled Sept. 24, 1963, Ser. No. 311,265 7 Claims. (Cl. 75-170) Thepresent invention relates to improved cobalt alloys and to methods ofmaking the same. More particularly, the present invention relates tocobalt base alloys having improved physical and metallurgicalproperties.

The present commercial cobalt alloys do not provide the strengthcapabilities under extreme conditions of high temperature and in ahighly oxidative environment as required in the neoteric nuclear,missile and space technologies. It is necessary under these conditionsto provide an alloy having high-temperature oxidation resistance,high-temperature strength and workability.

Accordingly, features and objects of this invention include theprovision of new composition with optimum strength and acceptableoxidation resistance at high temperatures.

Another object of the present invention is to provide an alloy of cobaltthat is strong and ductile while retaining sufiicient forgeability to beusefully workable.

A further object of the present invention is to provide an oxidationresistant alloy of cobalt that embodies the aforementioned properties.

A further object of the present invention is to provide a novel, wroughtcobalt base alloy that is superior in properties to those presently usedfor high temperature application.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying tables and graphs wherein:

FIG. 1 is a graphical presentation of the eifect of molybdenum additionon the properties of the wrought cobalt base;

FIG. 2 is a graphical presentation of the effect of ternary additionelements on the 1700 F. tensile properties of the base compositionCO-lSMO alloy.

The alloy which satisfies the objects of the present invention in itsbroadest aspects consists essentially of from 1 to 15 weight percentmolybdenum with the balance essentially all cobalt. The significance ofmolybdenum as a cobalt strengthener may be seen in FIG. 1. Primary solidsolubility in this system under the condition of heat treatment andtesting was limited to 9 weight percent molybdenum. The strength at 1700F. of the more highly alloyed material is, therefore, derived from bothsolution and precipitation hardening. The ductility of the alloy, whichmay also be seen in FIG. 1, was considered to be an important indicatorof the fabricability of the material.

Although the foregoing alloys satisfy all of the objects set forthabove, it was determined that by the addition of a third element to thebinary alloy composition, elevated temperature strength, forgeabilityand oxidation resistance could be improved. The effect of ternaryadditions on the 1700 F. tensile properties of the base compositioncobalt-15 weight percent molybdenum is shown in FIG. 2. The ternaryaddition of tantalum had the most significant beneficial effect upon theyield strength of the resulting alloy. The ternary addition of berylliumis particularly advantageous in achieving a ductile alloy. Ternaryadditions of 5 weight percent columbium or 8 3,243,289 Patented Mar. 29,1966 ice weight percent aluminum to the base composition cobalt- 15weight percent molybdenum resulted in small yet nevertheless beneficialincreases in both yield strength and ductility.

The oxidation resistance of the cobalt-molybdenum base alloys isimproved by the ternary addition of silicon or beryllium. The alloys ofcobalt-10 weight percent molybdenum-5 weight percent silicon, andcobalt-15 weight percent molybdenum-5 weight percent silicon areexceptionally oxidation resistant at 1700 F. The addition of up to 8percent aluminum to cobalt-l5 weight per cent molybdenum decreases thescaling rate of the alloy.

In the preparation of the cobalt base alloys, two grades of cobalt wereemployed, typical analyses of which are given below:

Rondell v Electrolytic Elements Cobalt Cobalt (Percent) (Percent) 99. 2999. 6 0. 28 01 20 0. 03 0. O5 nil 0. 01 0. 04 0. 05 0. 02 0. ()3 Trace0. 04 0. 01 Sulphur 0.01 0. 01

Electrolytic cobalt was found to be the more favorable base metal sincethis material is forgeable without the use of modifiers or specialmelting techniques. The alloys of the instant invention and the elementstherein were, in general, of equivalent or better purity than theelectrolytic cobalt with the exception that beryllium has a nominalpurity of 96 to 99%. The molybdenum, tantalum, columbium, and aluminumused were in the form of high purity sheet.

Alloys were prepared as ZSO-gram, pancake-shaped ingots approximately/2" 3" in diameter. There were arc-melted using a water-cooledtungsten-tipped electrode and a water-cooled, copper crucible in anargon atmosphere. The ingots were then hammer-forged to /2 in diameterrods from which test specimens were prepared.

Tensile tests were performed at room temperature and at 1700 F. at astrain rate of approximately 0.12 in./in./ minute. Before testing, allspecimens were sealed in evacuated bulbs, treated at 1700 F. for 24hours and air cooled.

Oxidation tests were performed on cylindrical specimens contained insmall individual porcelain crucibles. Weight gain data were recorded andafter oxidation the specimens were de-scaled mechanically andelectrolytically and reweighed. The data included in FIGS. 1 and 2disclosed the particularly advantageous high temperature yield strengthproperties of the ternary alloy cobalt-15 molybdenum-3 tantalum. Thedata also shows the overall strength improvement in a cobalt-molybdenumbase alloy of the ternary addition of up to 8 percent tantalum. Thestructure of the 3 percent tantalum alloy after heat treatment at 1700F. for 24 hours was found to contain a fine general precipitate ofintermetallic compound. Cobalt-molybdenum-tantalum alloys having agreater percentage of tantalum when heat treated were found to containmore precipitate in a coarser aggregation. As may be seen in the graphof FIG. 2, these alloys were of considerably lower strength and greaterductility than the cobalt-15 molybdenum-3 tantalum.

In the present invention and claims, the phrase up to shall be construedto include zero as the lower limit of the percentage range of optionalelements recited.

It will be apparent that new and useful alloys having desirablecharacteristics and properties have been disclosed. Itv isv thereforedesired to further describe the invention as set forth in the appendedclaims What is claimed is: v 1. A forgeable high-strength alloyconsisting essentially of from about 1 to 15 weight percent molybdenum,the

balance being essentially cobalt. v 2. A foregable oxidation resistantalloy consisting of from about 1 to 15 weight percent molybdenum, the

balance being essentially cobalt and beryllium.

3. A forgeable high-strength alloy consisting essentially of from about1 to 15 weight percent molybdenum,

3 weight percent tantalum,

the balance being cobalt.

4. A forgeable high-strength alloy consisting essentially of from about1 to 15 weight percent molybdenum,

up to about 8 weight percent tantalum,

the balance being essentially cobalt.

5. A forgeable oxidation resistant alloy consisting essentially of fromabout 1 to weight percent molybdenum,

up to 5 weight percent silicon,

the balance being essentially cobalt.

6. A forgeable oxidation resistant alloy consisting essentially of about1 to 15 weight percent molybdenum,

up to about 8 weight percent aluminum,

the balance being essentially cobalt.

7. A forgeable high-strength alloy consisting essentially of about 1 to15 weight percent molybdenum,

up to about 5 weight percent columbium,

the balance being essentially cobalt.

15 References Cited by the Examiner UNITED STATES PATENTS 1,588,5186/1926 Brace 75-171 1,949,313 2/1934 Koster 75170 2,250,850 7/1941Adamoli --170 2,981,620 4/1961 Brown et al. 75170 DAVID L. RECK, PrimaryExaminer. WINSTON A. DOUGLAS, Examiner. C. M. SCHUTZMAN, R. O. DEAN,Assistant Examiners.

1. A TORGEABLE HIGH-STRENGTH ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT1 TO 15 WEIGHT PERCENT MOLYBDENUM, THE BALANCE BEING ESSENTIALLY COBALT.